Ea f P Ap S dn Wdp Ws Ic ia tt SWD5149

where, besides variables defined above, Ic are the intake characteristics of the soil (mmh-1), ia is the application rate of the sprinkler (mmh-1), ti is the duration of the irrigation event (h), and SWD is the soil water deficit before the irrigation event (mm).

Equation (5.149) shows that the application efficiency depends not only on design and distribution uniformity but also on the management of the system by the farmers, including irrigation scheduling.

Most of the parameters in Eq. (5.149) are controlled by the designer. The pressure head P also depends on the functioning of the pressurized supply system. Dubalen [104], referring to Midi-Pyrennees, France, reports that only 52% of raingun systems and 58% of solid-set systems evaluated had the correct pressure at the sprinkler. This largely affects sprinkler discharges and makes it difficult to apply appropriate water depths. The duration of the application and the SWD are management variables controlled by the irrigator. However, when the farmer does not know the discharge or the application rate, he may not be able to correctly set the irrigation depth. The same study [104] shows that actual irrigation depths deviate by more than 20% from those claimed by the farmers in 46% of cases for raingun systems and 34% for solid-set systems.

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